Impacts of long-term fertilisation on plant functional traits and diversity of grasslands on Reunion Island

On Reunion Island, grassland is the second agricultural land cover. Grasslands are present in the different ecological contexts of the island (from tropical at sea level to temperate climate on the mountain area). The fertilisation inputs are quite high. The long-term impacts of fertilisation on the vegetation have been studied mainly for temperate grasslands and impacts on tropical grasslands are not well known. The species pool is different in the diverse climates. The functional trait approach allows us to compare the dynamics of communities with different species. We studied the impact of fertilisation (quantity and type of inputs) on grassland communities along a climatic gradient. Since 2004, ten different treatments of fertilisation with three replicates (organic and/or mineral inputs from 0 to 600 kg N ha -1) were applied on grassland in three different sites of the western part of Reunion Island (tropical site, temperate site and intermediate site). Three functional traits were measured: the specific leaf area (SLA), leaf dry matter content (LDMC) and vegetative height (H) in 2016. From these trait values, different variables were calculated (functional diversity, intraspecific variability indicators, etc.) and were compared between the different treatments and sites. The functional trait value was different between the three sites. The fertilisation affected only a few functional traits. These impacts were more important in the temperate climate than in the tropical one. This work contributes to our understanding of the long-term impact of fertilisation on the flora composition and can be used to propose adapted management of fertilisations (type or quantity).